1. Field of the Invention
The present invention relates to a satellite communication system for performing communication between terrestrial stations through a communication satellite, and particularly relates to a satellite communication system suitable for information collection of afflicted areas at the time of a disaster or the like.
2. Description of the Related Art
A telephone line network in which a satellite line is assigned in accordance with a call generated from a terrestrial station in a demand-on assign system has been known as a telephone line network using a satellite communication system for performing communication between very small terrestrial stations (Very Small Aperture Terminals: VSATS) through a communication satellite.
At the time of a disaster or the like, such as an earthquake or the like, it is very important to collect information of afflicted areas rapidly on taking effective means to meet the disaster.
However, at the time of a disaster or the like, such as an earthquake or the like, there is a case where a public telephone line network on the ground also suffers damages from extinction of communication lines or the like. There is also a case where telephone is apt to be out of order in a public telephone line network because of concentration of calls. It is therefore impossible to expect rapid collection of information of afflicted areas through telephone using such a public telephone line network.
On the other hand, in a telephone line network using satellite communication, the communication lines are wireless, and there is lower possibility that a disaster or the like disables the network from being used. In addition, because of using a satellite, it is possible to perform communication from a certain point with wider areas afflicted with the disaster.
That is, such a satellite communication system can be regarded as a system suitable for collecting information of afflicted area rapidly at the time of disaster. Even in a satellite communication system, however, if it is public network, it is inevitable that telephone is apt to be out of order because of concentration of calls. On the other hand, it makes the burden of cost, equipment and so on too heavy to provide terrestrial stations in various places or to build a satellite communication system which includes a call switching function for exclusive use for disaster. If the system does not include a call switching function, the system cannot be used flexibly at the time of disaster or the like. In addition, it can be considered that terrestrial stations provided in various places suffer damages so that they cannot be used at the time of disaster.